In the prior art process for preparing a vinyl chloride polymer batchwise in a reactor, a polymer slurry is discharged from the reactor at the end of polymerization. Since a polymer scale has built up on the reactor inner wall, the reactor must then be cleaned for subsequent reaction. The following cleaning steps were used in the prior art.
(1) After the reactor is opened by disconnecting a manhole lid, pressurized water (water pressure 150 kg/cm.sup.2 G=14.8 MPa.multidot.Gauge or higher) is injected through the manhole to wash away the polymer scale.
(2) After the reactor is opened by disconnecting a manhole lid, the worker enters the reactor and manually removes the polymer scale.
These cleaning steps (1) and (2) are performed while keeping the reactor open. This allows the unreacted monomer left in the reactor, though in a minor amount, to escape to the ambient air, causing air pollution. At the end of cleaning, the manhole must be closed again. A substantial labor and time are needed for opening and closing the manhole. The cleaning step deprives the process of continuity, leading to a lower productivity.
To solve these problems, the following cleaning steps were proposed.
(3) A nozzle is fixedly attached to the reactor at its top whereby pressurized water (water pressure 150 kg/cm.sup.2 G =14.8 MPa.multidot.Gauge or higher) is injected from the nozzle into the reactor for cleaning while keeping the reactor closed without substantial opening.
(4) A special solvent is poured into the reactor for cleaning while keeping the reactor closed without substantial opening.
Currently, large size polymerization reactors having an internal volume of greater than about 40 m.sup.3 are often used for the purpose of improving productivity. When the cleaning steps (3) and (4) are applied to such large size reactors, it is difficult from the apparatus and economical standpoints to fully clean the large size reactor in a closed state without substantially opening it. It is also difficult to solve the quality problem of vinyl chloride polymer products containing many fisheyes.